The biology of neoplasia is complex and associated with: 1) intrinsic aberrations of the neoplastic cell behavior; 2) changes in the surface membrane of the tumor cell with presentation of new or rearranged molecules; 3) the initiation of recocnitive events directed to the tumor cell surface; and 4) the character of the response of the host. This research program addresses selected issues in the biology of neoplasia, specifically; 1) The structure and the biology of a candidate tumor-specific antigen, mammary tumor-specific glycoprotein (MTGP). 2) The genomic basis for expression of MTGP and relationship of expression of MTGP to murine mammary tumor virus using characterized somatic cell hybrids and immunochemical analyses. 3) The tumor-specific antigen MTGP as a potential target for in vivo imaging of experimental breast carcinomas with monoclonal antibody synthesized by cloned hybridomas. 4) The recognition of this molecule and the host immune response to it. 5) Characterization and delineation of the genetic and functional restrictions in cellular cooperation required for immune induction of local procoagulant activity and examination of the bioregulatory properties of a discrete fibrinolytic peptide that is evolved, its effect on tumor cells and the immune attack against tumors. 6) The mollcular biology ofreceptor-mediated regulation of lymphoid function andthe immune response by discrete serum lipoproteins and lipoprotein subsets to mooe clearly delineate an aspect of regulation of the host immune response to neoplasia.